The present invention relates to a color image forming apparatus, and more particular to a correction table forming method for forming a correction table for correcting the color reproducibility and tone of a digital color copying machine, and to an image forming apparatus using the correction table.
In a conventional color copying machine using ink colors of Y (yellow), M (magenta), C (cyan) and K (black), properties relating to development, transfer, etc. will vary with a variation in environment and a variation with the passing of time, and it is thus difficult to maintain an optimal color image quality. With such varied properties, a copy image with high fidelity to the original cannot be reproduced.
General operators have difficulty in carrying out a work for adjusting a color balance, etc. and this work requires expertise. Only persons with skill can carry out the work. In order to solve this problem, for example, a gray patch and a black patch are generated from a mixture of the three colors. Color process parameters in an input-side color conversion section are corrected to effect gray balance adjustment. Thus, a variance, etc. in a reading apparatus is reduced. Subsequently, three-color gray patch data and black patch data are compared to effect γ correction of an output. Thereby, a difficult gray-balance adjustment is carried out. In this example, the three-color-mixture gray patch data and black patch data are compared to effect the γ correction of the output and thus the gray balance can be maintained. However, a tone of each record color cannot be maintained.
In order to maintain the tone of each color, Jpn. Pat. Appln. KOKAI Publication No. 5-169720, for instance, discloses a technique wherein a screen angle is applied to each pixel of each record color of a color image.
However, even where each color in a full-color mode is corrected, good reproducibility of the color of the human skin, for instance, cannot easily be obtained due to occurrence of moire. In addition, with this correction of each record color, good reproducibility of mono-color black cannot be obtained.